The present invention is directed to a method for analyzing the maintenance status of liquid-filled electric equipment.
The use of liquid-filled power transfer equipment is widespread in the electrical utility industry. These devices, including but not limited to transformers, load tap changers, tap changers, circuit breakers, off-load tap changers, on-load tap changers, switches, and the like, are usually filled with a dielectric insulating liquid.
Operational faults and the resulting degradation of insulating dielectric liquid occuring during the operation of liquid-filled electric power transfer equipment in the electrical utility industry are typically detected using a dissolved gas analysis technique. The presence of certain dissolved gases in the insulating liquid may indicate operational faults such as arcing, pyrolysis, corona discharge, and the like as well as leakage and other contamination. Typical gas analysis techniques can indicate the presence of gases including hydrogen, oxygen, nitrogen, carbon monoxide, carbon dioxide, methane, ethane, ethylene, acetylene, propane, and propylene. FIG. 1 illustrates a general testing protocol typically used in the electric utility industry to monitor the insulating liquid in electric power transfer equipment. In particular, the presence of hydrocarbon gases may indicate degradation of the insulating liquid filling the device, possibly due to electric discharges such as arcing or corona discharge, and consequent breakdown of the insulating capacity of the liquid. In addition to dissolved gas analysis, other tests are typically done to analyze the liquid, including tests to indicate moisture, interfacial tension, acid number, color, qualitative sediment, dielectric breakdown, power factor, and oxidation inhibitor content.
While these tests, along with the dissolved gas analysis, give a quantitative indication of the state of the insulating dielectric liquid, the test results generally do not give a good indication of the maintenance condition of the electric device. In particular, equipment breakdown indicated by operational faults such as arcing and corona discharge, and resulting deterioration of the equipment components, is not directly indicated by the presence of dissolved gases in the insulating liquid. Previous attempts to determine the equipment status include the use of atomic emission spectroscopy to measure the presence of trace metal contaminants in the insulating liquid. Trace metal analysis does not, however, give an accurate indication of the equipment condition. It would, therefore, be desirable to have an analysis method capable of accurately indicating the state of electric power transfer equipment, including the maintenance condition of the various equipment components.
It has now been found that an accurate indication of the maintenance state of an electric device and its insulating liquid is obtained using an analysis method comprising a particle analysis of suspended particles and sediment contained in the liquid. The analysis method can further comprise a chemical analysis of the insulating liquid. It has been surprisingly found that this analysis results in profiles of the liquid that give an accurate indication of the maintenance state of the electric device.
It is, therefore, an object of the present invention to provide a method of evaluating a liquid from a liquid-filled electric device, comprising the steps of:
obtaining a sample of said liquid; and
determining a particulate profile of said liquid, said particulate profile comprising a plurality of predetermined particulate characteristics.
This and other objects and advantages of the invention will become apparent to one of ordinary skill in the art upon reading the following specification and claims.